GLSL parser: Fix empty declaration qualifier checks The shader validation now does the same checks for qualifier combinations regardless of if a declaration is empty, as is specified. Some of these checks used to be in singleDeclarationErrorCheck, and have now been moved to a new function declarationQualifierErrorCheck. The other parts of singleDeclarationErrorCheck are under a renamed nonEmptyDeclarationErrorCheck. The patch also contains another related cleanup: Unnecessary symbol nodes won't be created for empty declarations any more. BUG=angleproject:2020 TEST=angle_unittests Change-Id: I1c864a5e151c52703926d8c550450b2561bfcbb2 Reviewed-on: https://chromium-review.googlesource.com/493227 Commit-Queue: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>